CRTs remain the typical self-luminous image display device, although plasma display panels (PDPs) are rapidly becoming widespread given the relative ease with which large, thin panels can be manufactured. While there are both alternative current (AC) PDPs and direct current (DC) PDPs, AC PDPs are superior in a number of respects including reliability and image quality, with three-electrode surface discharge PDPs in particular becoming widespread.
A three-electrode surface discharge PDP is constituted from a front substrate disposed parallel to a back substrate with a space therebetween. A plurality of display electrode pairs (scan and sustain electrodes) are formed in stripes on one side of the front substrate, with a dielectric film and a protective film layered to cover the electrode pairs. On the other hand, a plurality of data electrodes are formed in stripes on one side of the back substrate, with a dielectric film layered to cover the data electrodes. Barrier ribs are formed on the dielectric film between adjacent data electrodes, and a phosphor film is applied over the surface of the dielectric film and the sidewalls of the barrier ribs. Discharge cells are formed where the display electrode pairs and the data electrodes intersect in three-dimensional space, and image display is performed as a result of discharge emissions produced in discharge cells following the application of voltages to the electrodes.
Here, the display electrode pairs mostly adopt a structure in which each electrode is composed of a metal bus electrode layered on a transparent electrode in order to reduce electrical resistance. Furthermore, the protective film works to decrease the discharge voltage through the efficient emission of secondary electrons in the discharge cells, as well as to protect the display electrodes and dielectric film from high energy ions produced by the discharges. Moreover, the protective film is also required to hold wall charge on the surface thereof.
Magnesium oxide (MgO), combining excellent anti-sputtering characteristics with a large secondary electron emission coefficient, is generally employed as the material for the protective film formed in a thin-film process.
Reducing power consumption and suppressing discharge variability remain ongoing problems to be resolved in PDPs having the above features, with attempts having been made to resolve these problems from the angle of panel structure, drive method, and materials.
For example, patent document 1 discloses a PDP with a two-tiered structure in which a carbon nanotube (hereinafter “CNT”) layer and an MgO layer are sequentially layered over a dielectric film on the back substrate in order to improve the secondary electron emission coefficient. Thus, by forming an MgO layer over a CNT layer, MgO adheres to the unevenness of the CNT surface, increasing the surface area in comparison to a protective film made only from MgO, and dramatically increasing the secondary electron emission coefficient.
Increasing the secondary electron emission coefficient of the protective film in this way is considered effective in reducing the discharge firing voltage and improving luminous efficiency.
Patent Document 1: Japanese Patent Application Publication No. 2001-222944